The big one that has my mind totally boggled is Oregon Sunstone, which is a gem quality Plagioclase Feldspar.
I got a few little pieces for 25 cents each and run them through the fire in my normal way.
Being a feldspar i thought it would melt, or maybe turn white like other silicates i have tried (quartz, sodalite, agate etc).

To my surprise, it did neither of these things!!!!
They did not blow up, nor crack, but they did change color from a semi transparent yellow to almost a perfect clear!

I talked to a gem hound friend of mine and apparently a lot of rubys and diamonds are "heat treated" to help clarify them before they are cut and sold. Wierd!

Interesting read! I am a bit of a gemstone addict- but I like to use them through my house for their properties. (i am into metaphysical studies etc) I hold kyanite when meditating because of it's beautiful energy. Its sad to think of the gorgous kyanite being mined and ground up for glaze etc.
The obsidian would be pretty to see. One thing you might consider regarding heating these gems. a lot of them have air pockets and somewhat rare is an enhydro (small water chamber) Do you think some of these could be reasons for the exploding? If they were ground to a powder do you think they would react in other ways? Have you tried carnelian or mookait jasper? Those two are some of my favorites!!

Learning On my Kick wheel with my vintage Paragon (from the late 1960's)

As far as carnelian and japser i have not tested them specifically but i would be willing to be they would act as agates have.

As they are both "pretty much" just quartz (SiO2).
But you never know really!

I encourage people to experiment with this. My "standard way of firing a stone" is to toss a piece or two into a scrap pinchpot or bowl then COVER IT WITH A SCRAP SHELF OR PLATE OR BOWL OR SHARD.

Covering stone test is essential! Fast firing schedules and possible air/atmoshreric inclusions in the stone can very possibly make them blow up! If you can see a water inclusion in a stone, dont fire it! I had some quartz with carbon inclusions but i lost them before i could test them.

I always use small pieces typically no bigger than a pea; also it seems i use a lot of flakes because i will buy a big piece and then hit it with a hammer till i get some nice looking test pieces.

A friend of mine test fired a polished fluorite crystal about the size of a walnut and it BLEW UP bad............ pieces were everywhere, stuck onto glazed pieces, eaten into shelves and brick. He says he thinks it melted and spattered but i really dont think that was the case. Another important thing to note this was covered but only partially.

I am a Geology student and therefore i have good reference books into chemical compositions, i avoid anything with Chlorine, chemical water and also high refractory minerals (like kyanite) because i already know what they are going to do more or less.

Some of my favorite tests have been granites; all the different light and dark colored minerals included in the visible matrix melts differently. Find granite with very large grain sizes and some with small sizes and look at the difference. Or try some basalt, which, chemically is basically the same except the minerals in it have not seperated from each other in the matrix.

i am new to this posting, and new to pottery, but I am also a rock collector and had been wondering about the effects of gemstones in firing. Nice to know not to try it, I do not want explosions. I have all the stones you talked about and many more, kinda went a little overboard. But do you put pieces in your finished pieces? How would you attach them and how do you make the setting considering shrinking.

i dont really use them on my pieces a lot; just once or twice, usually i will just lay it on the glazed pot wherever i want it. A SMALL bit of fluorite on top of a clear glaze is cool looking. Obsidean is really sweet as well.